SummaryGalactooligosaccharides (GOS) are an important class of dietary prebiotics that exert benefi cial eff ects on intestinal microbiota and gut barrier function. In this study, high-purity GOS (HP-GOS) were investigated in vitro and in vivo and confi rmed as prebiotic ingredients in rat diet. HP-GOS were successfully produced using a two-step process, enzymatic hydrolysis and fermentation by yeast. They were found to serve as a good substrate and carbon source for supporting the growth of probiotic bacteria more eff ectively than other commercial GOS. Following administration of 1 % (by mass) of HP-GOS to rats, the growth of Bifi dobacterium bifi dum and B. longum in the gut increased most rapidly up to 12 h, and thereaft er the increase was slow. Therefore, 1 % HP-GOS was found to be acceptable for the growth of probiotic bacteria. Groups of animals that were orally administered HP-GOS and bifi dobacteria during the study, and the group administered HP-GOS during the 2nd (days 13-15) and 4th (days 28-30) period of the study had signifi cantly (p<0.05) higher numbers of bifi dobacteria in faeces than groups receiving a single dose of bifi dobacteria. HP-GOS aff ected the expression of genes encoding glucagon-like peptide-1 (GLP-1) and peptide YY (PYY). There was a signifi cant upregulation of GLP-1 and PYY mRNA with HP-GOS and bifi dobacteria intake. We propose that the prebiotic properties of HP-GOS are potentially valuable for the production of functional foods for human consumption.

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